Faculty Bibliography

PURPOSE/OBJECTIVE:Stability of correction is a major factor for successful refractive surgery. Intrastromal corneal rings were placed for the correction of low to moderate myopia beginning 10 years ago. The purpose of this study was to evaluate findings in patients 5 years after ring placement and to compare these findings with 1-year results to assess the stability of effect. METHODS:Seventy-two patients (113 eyes) with myopia (range, -0.75 to -4.50 diopters [D]) were treated with the placement of intrastromal corneal rings (360 degrees ), in a multicenter clinical trial between 1993 and 1994 under U.S. Food and Drug Administration phase II and phase III clinical trials. Six insert sizes were evaluated: 0.21, 0.25, 0.30, 0.35, 0.40, and 0.45 mm. The long-term results that were evaluated were uncorrected visual acuity, best spectacle-corrected visual acuity, cycloplegic refraction spherical equivalent at 5 years and proximity of this value to the target refraction determined preoperatively, induced manifest refraction cylinder, and slitlamp findings. RESULTS:Data at the 5-year follow-up showed that uncorrected visual acuity was 20/40 or better in 83% of eyes and 20/20 or better in 64% of eyes, compared to 88% and 43%, respectively, at the first year of follow-up. Only 7% of eyes lost two or more lines of preoperative best spectacle-corrected visual acuity at 5 years, compared to 11% at the first year. No eyes at the 1- or 5-year follow-up had a best spectacle-corrected visual acuity worse than 20/40. Cycloplegic refraction spherical equivalent was within 1.00 D of target refraction in 68% of eyes at 5 years, compared to 71% at the 1-year follow-up. Induced manifest refraction cylinder greater than 1.00 D was reduced to 5% of eyes in the fifth year, compared to 12% of eyes at year 1. CONCLUSIONS:Intrastromal corneal rings are a safe, effective, and stable method of correcting mild to moderate myopia, and most patients continue to be satisfied with the results after 5 years. There was no clinically significant change in refractive effect and the central corneas remained clear at the 5-year follow-up in all eyes studied. Further data are currently being collected for 10-year follow-up periods. It is hypothesized that the use of intrastromal corneal rings as a refractive option for mild to moderate myopia will be supported by these additional longitudinal data.

PURPOSE/OBJECTIVE:To evaluate and compare the wavefront characteristics of normal eyes with and without hydrogel soft contact lenses for correction of myopia. METHODS:Higher order aberrations (HOA) of 30 eyes of 15 soft contact lens users who had no ocular diseases other than myopia were quantified with a Nidek Marco three dimensional Wave wavefront analyzer. Zernike's polynomial was used to describe the wavefront measurements. Root mean square (RMS) values of the total HOAs, total coma, total trefoil and total spherical aberrations were obtained in the same eyes with and without soft contact lenses. We used paired sample t-test to analyze the data. RESULTS:Mean RMS values for all higher order aberration components with and without soft contact lenses were: total HOA 0.364 +/- 0.129 microm without lenses and 0.456 +/- 0.175 microm with lenses (P = 0.01), total coma 0.203 +/- 0.095 microm without lenses and 0.220 +/- 0.133 microm with lenses (P = 0.51), total trefoil 0.193 +/- 0.074 microm without lenses and 0.254 +/- 0.153 microm with lenses (P = 0.06), total spherical aberration 0.126 +/- 0.121 microm without lenses and 0.148 +/- 0.095 microm with lenses (P = 0.36). CONCLUSIONS:Wavefront analysis showed soft contact lenses for myopia induced a significant increase in total HOA. Though total coma, trefoil and spherical aberrations were also higher with contact lenses they were not statistically significant when individually evaluated and compared to values without contact lenses.

Transfer of nascent DNA from an RNA template (donor) to the homologous region of a second RNA template (acceptor) was studied. The templates were designed to assess the roles of the sequences proximal (3' relative to the transferring DNA) to the point of transfer. The donor template was primed with a specific 18 nucleotide DNA such that extension by reverse transcriptase to the end of the template produced a 79 nucleotide product. Homologous strand transfer and subsequent extension on the acceptors produced longer products allowing distinction between strand transfer and donor-directed synthesis. The donor and one particular acceptor shared a region of homology which included 8 tandem 5'-CAGU-3' repeats followed at the 3' end by a 17 nucleotide region of random homologous sequence. Derivatives of the acceptor either completely lacked the 17 nucleotide region or were progressively truncated resulting in a shorter region. With the acceptor lacking this region, prominent transfer products differing in length by 4 nucleotides were observed. Presumably this occurs because the transferring DNA can base-pair with several copies of the repeat elements of the acceptor. Addition of 5 or more of the 17 random nucleotides to the 3' end of the acceptor resulted in transfer products of essentially one length, and consistent with the transferring DNA correctly base-pairing with the 3' nucleotides. Results suggest that the transferring DNA interacts with the acceptor over several bases to form the most energetically stable hybrid duplex prior to extension on the acceptor. Hybrids formed from shorter interactions between the 3' end of the DNA and acceptor are either realinged prior to extension or precluded due to the mechanism of transfer.